1. Field of the Invention
This invention relates to a heat recovery device for a boiler assembly and, more particularly, to a method and apparatus for recovering excess heat from a boiler exhaust gas stream.
2. Description of the Related Art
The discharge of combustion waste gases from industrial boilers into the atmosphere without treatment is highly objectionable. Waste gases commonly include waste heat, nitrogen oxides, and other corrosive products. Nitrogen oxides act as atmospheric pollutants, so that it is desirable to treat such combustion waste gases in order to eliminate the nitrogen oxides prior to discharge. It is also desirable to recapture some of the waste heat to improve the overall energy efficiency of the system.
U.S. Pat. No. 4,350,669 discloses a process for controlling nitrogen oxides in combustion exhaust gases. The process includes adding an oxygen-containing hydrocarbon, its precursor, or both to exhaust gases. The hydrocarbon or the precursor oxidizes nitric oxide in the exhaust gas to form nitrogen dioxide in the presence of oxygen. The process includes an economizer that includes a bundle of tubes that serve as baffles.
U.S. Pat. No. 3,699,748 discloses a wet dust collector or scrubber having an inertial separator section for removing a substantial percentage of the dust particles from the treated gas stream. The scrubber includes porous packing subjected to flushing liquid to produce a concentrated fog. The remaining dust particles are assimilated into the fog. A second separator section removes the wet dust particles from the gas stream. The collector also includes three frusto-conical baffles or funnels positioned within a tubular casing.
U.S. Pat. No. 4,380,529 discloses a tubular fixed bed hydroprocessing reactor. The reactor is a fixed bed reactor with two phase gas and liquid flow. The reactor has at least one auxiliary bed of solid particles disposed above the main bed of solid particles. The auxiliary bed has separate liquid and gas bypasses comprised, of hollow tubing extending through the auxiliary bed to a distributor tray. The reactor also includes a flow distributor having a plurality of fluid distribution tubes.
U.S. Pat. No. 5,516,499 discloses a method and apparatus for reducing volatile organic compound emissions from waste gases. The waste gas is treated in a thermal reactor and is contacted with a catalyzed surface device in the gas stream within a thermal oxidizer. The catalyzed surface device has a catalyzed surface which contacts the waste gas and further oxidizes the waste gas. The apparatus also includes a catalytically-active flow modification device that has a flow straightener.
U.S. Pat. No. 6,348,178 discloses a system for reducing NOx in exhaust gases. The system uses hydrocarbons to autoignite and autothermally heat an exhaust gas from an industrial process, so that ammonia or HNCO selectively reduce NOx autocatalytically.
U.S. Pat. Nos. 5,198,196 and 5,389,343 disclose tubular reactor towers having removable catalyst trays.
U.S. Pat. Nos. 7,097,814 and 7,303,730 disclose an apparatus for treating exhaust gas from boilers. The apparatus includes a baffle structure and a duct having a catalyst layer.
U.S. Pat. No. 5,061,467 discloses a method and apparatus for removing pollutants from flue gases. The apparatus includes a conventional horizontal duct with a circular cross section. The duct feeds into a funnel shaped gas flow distributor that. The distributor feeds into a rectangular shaped duct with an enlarged cross section. The apparatus also includes a baffled curtain wall and a catalyst.
U.S. Pat. No. 4,003,711 discloses an apparatus and method for eliminating nitrogen oxides from combustion waste gases by injecting ammonia therein. The apparatus includes a boiler, an economizer, and a reaction tower. The reaction tower includes a plurality of baffle plates spaced from each other along the central portion of the reaction tower. The reaction tower also includes catalysts, which are preferably an alumina carrier or a silica gel carrier that includes a layer of ferrous sulfate.
The above-described references illustrate that the use of catalysts to treat exhaust gases is well known. Several of the devices also include baffles for redirecting the flow of exhaust gases through reactor devices. However, there is a need to improve the performance of these reactor devices to use catalysts and baffles in a more efficient manner.